Liquid ejection apparatus

ABSTRACT

A liquid ejection apparatus including: a liquid ejection head including an inside channel; a supply channel; a return channel; a supply device; an adjusting device; and a controller, wherein the controller starts a liquid circulation control for circulating liquid through the supply channel, the inside channel, and the return channel in order by controlling: the adjusting device such that a channel resistance value of the return channel is less than a predetermined maximum value; and the supply device to supply the liquid into the inside channel, wherein, when the liquid is circulated, the controller starts a liquid discharge control for discharging the liquid by increasing the channel resistance value, wherein, when the liquid is discharged, the controller starts a liquid-discharge stopping control for stopping the discharge by decreasing the channel resistance value, and wherein the controller controls the supply device such that a liquid amount supplied to the inside channel per unit time when the discharge is stopped is less than that in the liquid circulation control.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese Patent ApplicationNo. 2010-172237, which was filed on Jul. 30, 2010, the disclosure ofwhich is herein incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid ejection apparatus configuredto eject liquid from ejection openings.

2. Description of the Related Art

There is known an ink jethead configured to eject ink droplets from aplurality of ejection openings and perform a cleaning for the ejectionopenings by forcibly supplying the ink into ink channels in the ink-jethead by a pump and to discharge air bubbles and thickened or viscous inkremaining in portions of the ink channels which are located near theejection openings. For example, after a three-way valve is closed toclose and seal a discharging passage, a supply pump is operated topressurize the ink in the ink channels for a predetermined length oftime, thereby discharging the ink from nozzles to perform the cleaningof the nozzles.

SUMMARY OF THE INVENTION

In order to perform a cleaning of ejection openings by reliablydischarging ink from all the ejection openings, an ink pressure appliedto ink channels needs to be increased to a desired pressure. However, ifa relatively long time is required for the ink pressure in the inkchannels to reach the desired pressure after the pump starts to bedriven, the ink is discharged from the ejection openings in the order oftheir ink-discharge resistances or channel resistances, an ejectionopening having the lowest ink-discharge resistance first. This makes itimpossible to instantaneously discharge the ink from all the ejectionopenings at the same time. Thus, the ink is needlessly discharged fromthe ejection openings in the cleaning of the ejection openings. Further,since meniscus withstanding pressures of the ejection openings arelowered by adhesion of the discharged ink to portions defining theejection openings, the ink may leak from the ejection openings also byslight ink flow in the ink channels, leading to unnecessary inkdischarge.

This invention has been developed in view of the above-describedsituations, and it is an object of the present invention to provide aliquid ejection apparatus configured to efficiently discharge liquid andair bubbles and the like from ejection openings while preventingunnecessary consumption of the liquid.

The object indicated above may be achieved according to the presentinvention which provides a liquid ejection apparatus comprising: aliquid ejection head including: an inlet opening into which liquidflows; an outlet opening from which the liquid having flowed into theinlet opening flows; an inside channel communicating the inlet openingand the outlet opening with each other; and a plurality of ejectionopenings through which is ejected the liquid having flowed through aplurality of individual channels that are branched from the insidechannel; a tank storing the liquid to be supplied to the liquid ejectionhead; a supply channel communicating the tank and the inlet opening witheach other; a return channel communicating the tank and the outletopening with each other; a supply device configured to supply the liquidin the tank to the inside channel via the supply channel; an adjustingdevice configured to adjust a channel resistance value of the returnchannel between a predetermined minimum value and a predeterminedmaximum value; and a controller configured to control the supply deviceand the adjusting device, wherein the controller is configured to starta liquid circulation control for circulating the liquid through thesupply channel, the inside channel, and the return channel in order bycontrolling (i) the adjusting device such that the channel resistancevalue is less than the predetermined maximum value and (ii) the supplydevice to supply the liquid into the inside channel, wherein, when theliquid is circulated by the liquid circulation control, the controllerstarts a liquid discharge control for discharging the liquid from theplurality of the ejection openings by increasing the channel resistancevalue to a value larger than the channel resistance value in the liquidcirculation control, wherein, when the liquid is discharged by theliquid discharge control, the controller starts a liquid-dischargestopping control for stopping the discharge of the liquid from theplurality of the ejection openings, by decreasing the channel resistancevalue to a value less than the channel resistance value in the liquiddischarge control, and wherein the controller is configured to controlthe supply device such that a unit-time supply amount that is an amountof the liquid supplied to the inside channel per unit time at a timewhen the discharge of the liquid from the plurality of the ejectionopenings is stopped by the liquid-discharge stopping control is lessthan a unit-time supply amount in the liquid circulation control.

The object indicated above may also be achieved according to the presentinvention which provides a liquid ejection apparatus comprising: aliquid ejection head including: an inlet opening into which liquidflows; an outlet opening from which the liquid having flowed into theinlet opening flows; an inside channel communicating the inlet openingand the outlet opening with each other; and a plurality of ejectionopenings through which is ejected the liquid having flowed through aplurality of individual channels that are branched from the insidechannel; a tank storing the liquid to be supplied to the liquid ejectionhead; a supply channel communicating the tank and the inlet opening witheach other; a return channel communicating the tank and the outletopening with each other; a supply device configured to supply the liquidin the tank to the inside channel via the supply channel; an adjustingdevice provided at a predetermined area expanding from the outletopening of the inside channel, and configured to adjust a channelresistance value of the liquid in the predetermined area between apredetermined minimum value and a predetermined maximum value; and acontroller configured to control the supply device and the adjustingdevice, wherein the controller is configured to start a liquidcirculation control for circulating the liquid through the supplychannel, the inside channel, and the return channel in order bycontrolling (i) the adjusting device such that the channel resistancevalue is less than the predetermined maximum value and (ii) the supplydevice to supply the liquid into the inside channel, wherein, when theliquid is circulated by the liquid circulation control, the controllerstarts a liquid discharge control for discharging the liquid from theplurality of the ejection openings by increasing the channel resistancevalue to a value larger than the channel resistance value in the liquidcirculation control, wherein, when the liquid is discharged by theliquid discharge control, the controller starts a liquid-dischargestopping control for stopping the discharge of the liquid from theplurality of the ejection openings, by decreasing the channel resistancevalue to a value less than the channel resistance value in the liquiddischarge control, and wherein the controller is configured to controlthe supply device such that a unit-time supply amount that is an amountof the liquid supplied to the inside channel per unit time at a timewhen the discharge of the liquid from the plurality of the ejectionopenings is stopped by the liquid-discharge stopping control is lessthan a unit-time supply amount in the liquid circulation control.

In the image liquid ejection apparatuses constructed as described above,air bubbles, foreign matters, and the like remaining in the insidechannel can be discharged into the tank by the liquid circulation whilepreventing the liquid from leaking from the ejection openings. Further,the channel resistance value is increased by the adjustment of theadjusting device in this state to momentarily increase a pressure in theinside channel, whereby the liquid in the inside channel flows into theindividual channels so as to be discharged from the ejection openings.In this operation, a relatively high pressure is applied to all theejection openings from the start of the liquid discharge control todischarge the liquid in the ejection openings. Accordingly, it ispossible to efficiently discharge thickened liquid in the ejectionopenings, the air bubbles, and the foreign matters, and it is possibleto prevent the liquid from being discharged needlessly. Further, theunit-time supply amount at an end of the liquid discharge control isless than that in the liquid circulation control. Thus, even where ameniscus withstanding pressure of a meniscus formed in the ejectionopenings has been lowered because the liquid discharged in a previousdischarging has adhered to defining portions of the ejection openings,it is possible to prevent the liquid from leaking from the ejectionopenings after the end of discharging of the liquid.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features, advantages, and technical and industrialsignificance of the present invention will be better understood byreading the following detailed description of an embodiment of theinvention, when considered in connection with the accompanying drawings,in which:

FIG. 1 is a plan view generally showing an ink-jet printer as oneembodiment of the present invention;

FIG. 2 is a cross-sectional view showing an ink-jet head and an inksupply unit shown in FIG. 1;

FIG. 3 is a plan view showing a head main body shown in FIG. 2;

FIG. 4 is an enlarged view showing an area enclosed by a one-dot chainline shown in FIG. 3;

FIG. 5 is a partial cross-sectional view showing the ink-jet head shownin FIG. 4;

FIG. 6 is a graph showing operational characteristics of a purging pumpshown in FIG. 2;

FIG. 7 is a functional block diagram of a controller shown in FIG. 1;

FIG. 8 is a waveform chart of an ejection driving signal produced by ahead controller shown in FIG. 7;

FIG. 9 is a view showing a flow of ink when the ink is circulated by acirculation-and-purging controller shown in FIG. 7;

FIG. 10 is a view showing an operational sequence of the ink jet printershown in FIG. 1;

FIG. 11 is a graph showing changes of an ink-flow amount in a purgingoperation executed by the circulation-and-purging controller shown inFIG. 7;

FIG. 12 is a view showing an operational sequence of an ink jetprinteras a modification of the present embodiment; and

FIG. 13 is a view for explaining another modification.

DETAILED DESCRIPTION OF THE EMBODIMENT

Hereinafter, there will be described an embodiment of the presentinvention by reference to the drawings.

As shown in FIG. 1, an ink jetprinter 101 as one example of a liquidejection apparatus includes: (a) a sheet conveyance unit 20 configuredto convey a sheet P from an upper side toward a lower side in FIG. 1;(b) four ink jetheads 1 (each as one example of liquid ejection head)configured to eject droplets of inks of respective four colors, namely,black, magenta, cyan, and yellow onto the sheet P conveyed by theconveyance unit 20; four ink supply units 10 configured to respectivelysupply the inks to the ink-jet heads 1; a maintenance unit 31 configuredto perform a maintenance for ink jetheads 1; and a controller 16configured to control entire operations of the ink jet printer 101. Itis noted that, in the present embodiment, a sub-scanning direction is adirection parallel to a conveyance direction in which the conveyanceunit 20 conveys the sheet P, and a main scanning direction is adirection perpendicular to the sub-scanning direction and along ahorizontal plane.

The conveyance unit 20 includes two belt rollers 6, 7 and an endlesssheet conveyance belt 8 wound around the rollers 6, 7. The belt roller 7is a drive roller that is rotated by a drive power from a conveyancemotor, not shown. The belt roller 6 is a driven roller that is rotatedin accordance with the running or rotation of the conveyance belt 8which is caused by the rotation of the belt roller 7. The sheet P placedon an outer circumferential face of the conveyance belt 8 is conveyedtoward the lower side in FIG. 1.

The four ink-jet heads 1 each extends in the main scanning direction andare disposed in parallel with one another in the sub-scanning direction.That is, the ink-jet printer 101 is a line-type color ink-jet printer inwhich a plurality of ejection openings 108 through which the inkdroplets are ejected are arranged in the main scanning direction. Alower face of each ink jethead 1 functions as an ejection face 2 a inwhich the plurality of the ejection openings 108 are formed (see FIGS.2-4).

An outer circumferential face of an upper portion of the conveyance belt8 and the ejection faces 2 a face and parallel with each other. When thesheet P conveyed on the conveyance belt 8 passes through positions justunder the four ink jet heads 1, the ink droplets of four colors areejected in order from the respective ink jet heads 1 onto an upper faceof the sheet P, whereby a desired color image is formed on the sheet P.

Each of the ink supply units 10 is connected to a left end portion ofthe lower face of a corresponding one of the ink-jet heads 1 in FIG. 1so as to supply the ink to the corresponding ink-jet head 1.

The maintenance unit 31 includes four wiper members 32. Each of thewiper members 32 is an elastic member for wiping the ejection face 2 aof a corresponding one of the ink jetheads 1 in a wiping operation of amaintenance operation which will be described below. Each wiper member32 is reciprocable by an actuator, not shown, in the main scanningdirection (indicated by an arrow in FIG. 1).

There will be next explained the ink-jet heads 1 in detail withreference to FIG. 2. As shown in FIG. 2, each ink-jet head 1 includes areservoir unit 71 and a head main body 2.

The reservoir unit 71 is a channel defining member that is fixed to anupper face of the head main body 2 and supplies the ink to the head mainbody 2. The reservoir unit 71 has an ink inlet channel 72 (as oneexample of an inside channel), ten ink outlet channels 75, and adischarge channel 73 (as another example of an inside channel) formedtherein. It is noted that only a single ink outlet channel 75 is shownin FIG. 2.

The ink inlet channel 72 is a channel into which the ink from the inksupply unit 10 flows via an inlet opening 72 a opened in a lower face ofthe reservoir unit 71. The ink inlet channel 72 functions as an inkreservoir for temporarily storing the flowed ink. In an inner wall faceof the ink inlet channel 72, there is formed a hole 72 b formed throughan outer wall face of the reservoir unit 71. The hole 72 b is sealed bya flexible resin film 76 from a side of the hole 72 b which is nearer tothe outer wall face of the reservoir unit 71. That is, the resin film 76partly constitutes the inner wall face of the ink inlet channel 72. Inother words, at least a part of the inner wall face of the ink inletchannel 72 is formed of a flexible material. The resin film 76 isdisplaced according to changes of a pressure of the ink in the ink inletchannel 72, functioning as a damper for restraining the changes of theink pressure. Using the resin film 76 enables to provide the damper atlow cost. It is noted that, in a normal recording, the resin film 76slightly projects toward an inside of the ink inlet channel 72. To theouter wall face of the reservoir unit 71 is fixed a plate-likerestraining member 77 so as to cover the hole 72 b, thereby restrainingthe resin film 76 from projecting toward an outside of the reservoirunit 71. As a result, it is possible to prevent the resin film 76 frombeing broken by being excessively displaced when the ink pressure in theink inlet channel 72 becomes excessively high. In the restraining member77 is formed an air communicating hole 77 a that always keeps a pressurebetween the restraining member 77 and the resin film 76 at anatmospheric pressure. This facilitates the displacement of the resinfilm 76.

The ink outlet channels 75 communicate with the ink inlet channel 72 viaa filter 75 a and with ink supply openings 105 b formed in an upper faceof a channel unit 9 (see FIG. 3). The filter 75 a extends in a directionin which the ink flows in the ink inlet channel 72 (i.e., in therightward and leftward direction in FIG. 2). In the normal recording,the ink supplied from the ink supply unit 10 flows into the ink inletchannel 72, then passes through the ink outlet channels 75, and finallyis supplied from the ink supply openings 105 b to the channel unit 9.

The discharge channel 73 communicates with the ink inlet channel 72 at aportion thereof located on an upstream side of the filter 75 a and isconnected to the ink supply unit 10 via an outlet opening 73 a formed inthe lower face of the reservoir unit 71.

In a lower inner wall face of the discharge channel 73, there is formeda hole 73 b formed through the outer wall face of the reservoir unit 71.The hole 73 b is sealed by a flexible resin film 78 from a lower side ofthe hole 73 b, i.e., from a side of the hole 73 b which is nearer to theouter wall face of the reservoir unit 71. That is, the resin film 78partly constitutes the inner wall face of the discharge channel 73. Inother words, at least a part of the inner wall face of the dischargechannel 73 is formed of a flexible material. The resin film 78 isdisplaced according to changes of a pressure of the ink in the dischargechannel 73, functioning as a damper for restraining the changes of theink pressure. Using the resin film 78 enables to provide the damper atlow cost. It is noted that, in the normal recording, the resin film 78slightly projects toward an inside of the discharge channel 73. To thelower outer wall face of the reservoir unit 71 is fixed a plate-likerestraining member 79 so as to cover the hole 73 b, thereby restrainingthe resin film 78 from projecting toward an outside of the reservoirunit 71. As a result, it is possible to prevent the resin film 78 frombeing broken by being excessively displaced when the ink pressure in thedischarge channel 73 becomes excessively high. In the restraining member79 is formed an air communicating hole 79 a that always keeps a pressurebetween the restraining member 79 and the resin film 78 at theatmospheric pressure. This facilitates the displacement of the resinfilm 78. In ink circulation which will be described below, the inksupplied from the ink supply unit 10 flows into the ink inlet channel 72via the inlet opening 72 a, then passes from the ink inlet channel 72through the discharge channel 73, and finally returns to the ink supplyunit 10 via the outlet opening 73 a (see FIG. 9).

There will be next explained the head main body 2 in more detail withreference to FIGS. 3-5. It is noted that, in FIG. 4, pressure chambers110, apertures 112, and the ejection openings 108 are illustrated bysolid lines for easier understanding purposes though these elementsshould be illustrated by broken lines because these elements are locatedunder actuator units 21.

As shown in FIGS. 3-5, the head main body 2 includes the channel unit 9and the four actuator units 21 fixed to the upper face of the channelunit 9. The channel unit 9 has ink channels including the pressurechambers 110 and so on. The actuator units 21 include a plurality ofunimorph actuators respectively corresponding to the pressure chambers110 so as to selectively apply ejection energy to the ink in thepressure chambers 110.

The channel unit 9 is a stacked body constituted by a plurality of metalplates 122-130 formed of stainless steel and positioned and stacked oneach other. The upper face of the channel unit 9 has the ten ink supplyopenings 105 b opened therein which communicate respectively with theink outlet channels 75 of the reservoir unit 71 (see FIG. 2). As shownin FIG. 3, in the channel unit 9 are formed a plurality of manifoldchannels 105 and a plurality of sub-manifold channels 105 a. Each of theink supply openings 105 b communicates with a corresponding one of themanifold channels 105, and each of the sub-manifold channels 105 a isincluded in a corresponding one of the manifold channels 105. Further,as shown in FIG. 5, in the channel unit 9 is formed a plurality ofindividual ink channels 132 each branched from a corresponding one ofthe sub-manifold channels 105 a and extending to a corresponding one ofthe ejection openings 108 opened in the ejection face 2 a via acorresponding one of the pressure chambers 110. In the ejection face 2a, the ejection openings 108 are formed in matrix.

There will be next explained flow of the ink in the channel unit 9. Asshown in FIGS. 3-5, in the normal recording, the ink supplied from theink outlet channels 75 of the reservoir unit 71 to the ink supplyopenings 105 b is distributed to the sub-manifold channels 105 a of themanifold channels 105. The ink in the sub-manifold channels 105 a flowsinto the individual ink channels 132 including the respective apertures112 and the respective pressure chambers 110 and reaches the respectiveejection openings 108 through the respective individual ink channels132.

There will be next explained the ink supply unit 10 in detail. As shownin FIG. 2, each ink supply unit 10 includes: (a) a sub-tank 80; (b) anink replenish tube 81 connected to the sub-tank 80; (c) a replenish pump91 and a replenish valve 92 provided on the ink replenish tube 81; (d)an ink supply tube 82 as one example of a supply channel and an inkreturning tube 83 as one example of a return channel; (e) a purging pump86 (as one example of a supply device) provided on the ink supply tube82; (f) a circulation valve 87 as one example of an adjusting deviceprovided on the ink returning tube 83; and (g) an air communicatingvalve 88 as one example of an air communication device connected to thesub-tank 80.

The sub-tank 80 is for storing the ink to be supplied to the ink-jethead 1. When an amount of the ink in the sub-tank 80 becomes small, thereplenish valve 92 is opened and the replenish pump 91 is driven,thereby replenishing the ink stored in an ink tank 90 to the sub-tank 80via the ink replenish tube 81. The air communicating valve 88communicates, in its open state, an inside of the sub-tank 80 with anambient air or interrupts, in its closed state, the communication of thesub-tank 80 with the ambient air. In the normal recording, the aircommunicating valve 88 is open, so that the inside of the sub-tank 80and the ambient air communicate with each other. As a result, an airpressure in the sub-tank 80 is always kept at an atmospheric pressureregardless of the amount of the ink stored in the sub-tank 80, ensuringstable ink supply.

One end of the ink supply tube 82 is connected to the sub-tank 80, andthe other end thereof is connected to the inlet opening 72 a of thereservoir unit 71 via a joint 82 a. Thus, the ink in the sub-tank 80 issupplied to the ink inlet channel 72 of the reservoir unit 71 via theink supply tube 82. The purging pump 86 functions as a supply portionwhich is driven to forcibly supply the ink in the sub-tank 80 to the inkinlet channel 72 via the ink supply tube 82. Further, the purging pump86 functions as a check valve which prevents the ink from flowing fromthe joint 82 a toward the sub-tank 80 in the ink supply tube 82. It isnoted that, even where the purging pump 86 is stopped, the ink in thesub-tank 80 can be supplied to the reservoir unit 71 by flowing throughthe ink supply tube 82. The purging pump 86 is a three-phase diaphragmpump as a volume pump, and as shown in FIG. 6, three diaphragms aredriven in different phases to discharge the ink, thereby restraining apressure variation upon the ink supply.

As shown in FIG. 2, one end of the ink returning tube 83 is connected tothe sub-tank 80, and the other end thereof is connected to the outletopening 73 a of the reservoir unit 71 via a joint 83 a. The circulationvalve 87 is an adjustment portion configured to adjust a channelresistance value of the ink returning tube 83 between a predeterminedminimum value (in an open state of the circulation valve 87) and apredetermined maximum value (in a closed state of the circulation valve87). It is noted that, in the present embodiment, the circulation valve87 is an open-and-close valve for changing between (a) its open state inwhich the flow of the ink is not interrupted at all and (b) its closedstate in which the flow of the ink is completely interrupted orinhibited, but the circulation valve 87 may be a channel controllingvalve capable of adjusting the channel resistance value at any value.

There will be next explained the controller 16 with reference to FIG. 7.The controller 16 includes: a Central Processing Unit (CPU); anElectrically Erasable and Programmable Read Only Memory (EEPROM) thatrewritably stores programs to be executed by the CPU and data used forthe programs; and a Random Access Memory (RAM) that temporarily storesdata when the program is executed. The controller 16 includes variousfunctioning sections which are constituted by cooperation of thesehardwares and softwares in the EEPROM with each other. The controller 16is configured to control entire operations of the ink-jet printer 101and includes: a conveyance controller 41; an image-data storage portion42; a head controller 43; a non-ejection-time detecting section 46; acirculation-and-purging controller 44; and a maintenance controller 45.

The conveyance controller 41 controls the conveyance motor of theconveyance unit 20 such that the sheet P is conveyed in the conveyancedirection at a predetermined speed. The image-data storage portion 42stores therein image data relating to an image to be recorded on thesheet P.

In the normal recording, the head controller 43 produces an ejectiondriving signal on the basis of the image data and supplies the producedejection driving signal to the actuator units 21. As shown in FIG. 8,the ejection driving signal is a signal including a pulse that changesfrom an electric potential V1 to a ground potential V0 for apredetermined length of time in a single recording cycle. This pulsewidth t is equal to a length of time in which a pressure wave istransmitted through a distance AL (Acoustic Length) extending from anoutlet of the sub-manifold channel 105 a to the ejection opening 108. Itis noted that a waveform in FIG. 8 is a waveform corresponding toejection of a small ink droplet and having a single pulse. A waveformcorresponding to a medium-size ink droplet is constituted by successivetwo pulses, and a waveform corresponding to a large ink droplet isconstituted by successive three pulses.

On the basis of an ink ejection history, the non-ejection-time detectingsection 46 detects, for each ink jethead 1, an elapsed time from thelast (most recent) ejection of the ink droplet from the ejection opening108 to a current time. Specifically, the non-ejection-time detectingsection 46 detects the elapsed time on the basis of the ejection drivingsignal outputted from the head controller 43 or the data stored in theimage-data storage portion 42.

In the maintenance operation which will be described below, thecirculation-and-purging controller 44 controls operations of the purgingpump 86, the circulation valve 87, and the air communicating valve 88 ofeach ink supply unit 10. Specific controls of thecirculation-and-purging controller 44 will be described below. It isnoted that the circulation-and-purging controller 44 also controls thereplenish pump 91 and the replenish valve 92 for the ink replenishing,but these are omitted in FIG. 7.

The maintenance controller 45 controls the maintenance unit 31 in themaintenance operation which will be described below.

There will be next explained the maintenance operation with reference toFIGS. 9-11. The maintenance operation is an operation for performing themaintenance of the ink jetheads 1 and is started when the ink jetprinter101 is booted up, when a standby time during which the recording has notbeen performed has passed a specific length of time, and when a commandis inputted by a user, for example. During the standby state and thenormal recording, the purging pump 86 is stopped, the circulation valve87 is closed, the air communicating valve 88 is open, the replenish pump91 is stopped, and the replenish valve 92 is closed (see FIG. 2).

As shown in FIGS. 9 and 10, when the maintenance operation is started,the circulation-and-purging controller 44 opens the circulation valve 87(at a time t1) and then closes the air communicating valve 88 and drivesthe purging pump 86 at the same time (at a time t2, a liquid circulationcontrol is started). It is noted that the replenish pump 91 is stopped,and the replenish valve 92 is closed during the maintenance operation.

As a result, the ink in the sub-tank 80 is forcibly supplied to the inkinlet channel 72 via the ink supply tube 82. Since the circulation valve87 is open at this time, a channel resistance in a passage from the inkinlet channel 72 to the sub-tank 80 via the discharge channel 73 and theink returning tube 83 is less than that in a passage from the ink inletchannel 72 to the ejection openings 108 via the ink outlet channels 75and the manifold channels 105. Thus, the ink supplied to the ink inletchannel 72 passes through the discharge channel 73 and the ink returningtube 83 in order and returns to the sub-tank 80 (that is, the inkcirculation (liquid circulation) is performed) without flowing into theink outlet channels 75. When the ink circulation is performed, thepressure of the ink rises in a channel from the purging pump 86 to thesub-tank 80 in the circulation passage. Thus, by the ink flowing by theink circulation, air bubbles and foreign matters remaining in the inkinlet channel 72, especially the air bubbles and the foreign mattersbuilt up on the filter 75 a, are carried through the discharge channel73 and the ink returning tube 83 in order together with the ink, so thatthe air bubbles and the foreign matters are trapped in the sub-tank 80.

In order to efficiently move the air bubbles and the foreign matters tothe sub-tank 80 by the ink circulation, there is a need to increase anamount (an ink-flow amount) of the flow of the ink to be supplied fromthe purging pump 86 per unit time (hereinafter may be referred to as“unit-time supply amount”) in a range not higher than an amount(meniscus-break ink-leakage amount) of the ink at a timing when the inkstarts to leak or flow from the ejection openings 108 by a break ofmeniscus (meniscus break) of the ink in the ejection openings 108 (seeFIG. 11). That is, the amount of the ink supplied by the purging pump 86during the ink circulation is set as large as possible in a range inwhich the meniscus of the ink formed in the ejection openings 108 is notbroken and the ink is not discharged from the ejection openings 108. Itis noted that the meniscus-break ink-leakage amount is a value obtainedby actual measurement or a value calculated from a channel structure ofthe ink jethead 1, a height relationship between the ink jethead 1 andthe sub-tank 80 in the ink-jet printer 101, viscosity of the ink, and/orso on. The meniscus-break ink-leakage amount is stored in advance. It isnoted that the unit-time supply amount is set at an amount that issmaller than the meniscus-break ink-leakage amount and that is obtainedby reducing a specific amount from the meniscus-break ink-leakageamount. This specific amount functions as a margin of the ink-flowamount such that the meniscus break does not occur even if a state ofthe meniscus has been changed by pulsation of the ink flow caused by thepurging pump 86 and/or changes of environments such as ambienttemperature and humidity. Further, when the purging operation isperformed from the ejection openings 108 later, the ink flow in thedischarge channel 73 is suddenly stopped or closed, whereby the inkpressures in the discharge channel 73 and the ink inlet channel 72suddenly rise. The ink-flow amount per unit time is set at an amountequal to or larger than an ink amount (recoverable ink-flow amount) thatcan discharge the air bubbles and the foreign matters remaining in theindividual ink channels from the ejection openings 108 together with theink by this rise of the ink pressures. It is noted that the recoverableink-flow amount is a value obtained by actual measurement and stored inadvance. From another point of view, where the driving of the purgingpump 86 is started in the state in which the circulation valve 87 isclosed such that the ink-flow amount is the recoverable ink-flow amount,an ink amount capable of discharging the air and the foreign mattersremaining in the individual ink channels from all the ejection openings108 together with the ink can be also referred to as the recoverableink-flow amount. That is, where the purging pump 86 is driven with theink whose ink amount is less than the recoverable ink-flow amount, theink may continue to be discharged only from ejection openings 108respectively communicating with individual ink channels 132 containingrelatively small amounts of air bubbles and thickened or viscous ink. Inthis case, even if a period for discharging the ink is made longer, theink may not be discharged from all the ejection openings 108 togetherwith the air and the foreign matters.

It is noted that, in the ink circulation, the ink pressures in the inkinlet channel 72 and the discharge channel 73 are relatively high whencompared with in the normal recording, and accordingly the resin film 76in the ink inlet channel 72 is held in close contact with therestraining member 77, and the resin film 78 in the discharge channel 73is held in close contact with the restraining member 79.

In the period during which the air communicating valve 88 is closed inthe ink circulation, a negative pressure is produced in the sub-tank 80.The ink in the ink inlet channel 72 is thus sucked into the sub-tank 80via the discharge channel 73, making it difficult for the ink to flowinto the ink outlet channels 75 when compared with the case where theair communicating valve 88 is open. As a result, the pressure in the inkinlet channel 72 is lowered, causing less meniscus break. Thus, whencompared with the case where the air communicating valve 88 is open, theunit-time supply amount can be made larger until the pressure in the inkinlet channel 72 becomes closer to a pressure (meniscus-break pressure)at which the meniscus is broken. That is, assuming that the pressure inthe ink inlet channel 72 is constant during the circulation, where theair communicating valve 88 is closed, the ink-flow amount is larger inthe case where the air communicating valve 88 is open. Further, wherethe air communicating valve 88 is closed, the pressure in the ink inletchannel 72 during the purging period can be made larger than in the casewhere the air communicating valve 88 is open. Accordingly, it ispossible to efficiently discharge the air bubbles and the foreignmatters remaining in the individual ink channels from the ejectionopenings 108 together with the ink. In the present embodiment, theunit-time supply amount is an amount during the ink circulation that islarger than a maximum amount in which the ink does not leak from theejection openings 108 per unit time where the air communicating valve 88is open and that is equal to or less than a maximum amount in which theink does not leak from the ejection openings 108 per unit time where theair communicating valve 88 is closed. It is noted that, in FIG. 10, asolid-line waveform and a broken-line waveform indicate pressure changesin the ink inlet channel 72, specifically, the solid-line waveformindicates the pressure changes in the channel where the unit-time supplyamount is made larger as described above in the state in which the aircommunicating valve 88 is closed during the ink circulation (i.e., inthe case of the present embodiment), and the broken-line waveformindicates the pressure changes in the channel where the aircommunicating valve 88 is open during the ink circulation (noted thatthe unit-time supply amount is not made larger).

The purging (liquid discharge) operation is started (at a time t3, aliquid discharge control is started), when the ink circulation has beenperformed for a length of time enough to remove the air and the foreignmatters remaining in the ink inlet channel 72 from at least the inkinlet channel 72, in a state in which the ink-flow amount from thepurging pump 86 per unit time is equal to or larger than the recoverableink-flow amount. When the purging operation is started, as shown inFIGS. 10 and 11, the circulation-and-purging controller 44 closes thecirculation valve 87 and opens the air communicating valve 88 at thesame time. Thus, the ink flow in the discharge channel 73 is suddenlystopped by the circulation valve 87, whereby the ink pressures in thedischarge channel 73 and the ink inlet channel 72 suddenly rise. As aresult, the ink supplied to the ink inlet channel 72 flows into the inkoutlet channels 75 without flowing into the discharge channel 73, andthen the ink passes through the manifold channels 105 and the individualink channels 132 in order and is discharged from the ejection openings108. The discharged ink is received by a waste-ink tray, not shown.

Since the purging operation is started by closing the circulation valve87 in the state in which the ink circulation is being performed suchthat the ink-flow amount from the purging pump 86 per unit time is equalto or larger than the recoverable ink-flow amount (noted that thispurging operation may be hereinafter referred to as “impact purge”), theink pressure in the ink inlet channel 72 is relatively high from a pointin time just after the purging operation is started, whereby thethickened ink in the ejection openings 108 and the remaining air bubblesand foreign matters can be efficiently discharged from the ejectionopenings 108. If the impact purge is not performed, that is, if thepurging pump 86 starts to be driven in the state in which thecirculation valve 87 is closed without circulating the ink, to dischargethe ink from the ejection openings 108 (a conventional technique), alength of time required for an ink pressure in each of the individualink channels 132 to exceed a pressure at which the ink is dischargedfrom all the ejection openings 108 becomes longer, and the ink isneedlessly discharged from the ejection openings 108 until the length oftime has been passed. That is, since the ink is discharged from only theejection openings 108 respectively communicating with the individual inkchannels 132 containing relatively small amounts of air bubbles andthickened ink, the ink is discharged unnecessarily. Further, in theabove-described embodiment, the circulation valve 87 is closed, and theair communicating valve 88 is opened simultaneously. Thus, the pressurein the sub-tank 80 forcibly becomes the atmospheric pressure, therebypreventing the pressure in the sub-tank 80 from lowering in accordancewith the discharging of the ink. Where the communication of the sub-tank80 with the ambient air is interrupted when the ink is discharged, theink does not flow into the sub-tank 80, and accordingly a large amountof the negative pressure may be produced in the ink when the ink isdischarged, thereby hindering the operation of the purging pump 86, butwhere the sub-tank 80 is communicated with the ambient air when the inkis discharged, it is possible to avoid the hindrance to the operation ofthe purging pump 86.

When a predetermined purging amount of the ink has been discharged fromthe ejection openings 108, the circulation-and-purging controller 44stops the driving of the purging pump 86 (at a time t4, aliquid-discharge stopping control is started). After the driving of thepurging pump 86 has been stopped, the unit-time supply amount decreasesas time passes. When the purging pump 86 has been stopped and theunit-time supply amount has become a predetermined amount that issmaller than the unit-time supply amount in the ink circulation, inother words, when the unit-time supply amount has become a predeterminedamount that is less than the unit-time supply amount in the inkcirculation indicated by a solid line in FIG. 11 and less than therecoverable ink-flow amount, the circulation-and-purging controller 44opens the circulation valve 87 and closes the air communicating valve 88at the same time, and stops the purging operation (at a time t5). It isnoted that the predetermined purging amount is determined by theink-flow amount of the purging pump 86 per unit time and a length of thepurging period. The ink-flow amount per unit time and the length of thepurging period for discharging the predetermined purging amount of theink are obtained by experiment and stored in advance. Thecirculation-and-purging controller 44 makes the circulation periodlonger and the purging amount larger in accordance with increase in atemperature detected by a temperature sensor 35 or increase in a lengthof the elapsed time detected by the non-ejection-time detecting section46.

As described above, by performing the ink circulation and the purgingoperation in order, the air bubbles and the foreign matters remaining inthe ink inlet channel 72 can be discharged to an outside of the ink-jetheads 1 without flowing into downstream-side channels (e.g., themanifold channels 105, the individual ink channels 132, and the like).

After the unit-time supply amount has become zero by stopping thedriving of the purging pump 86, the circulation-and-purging controller44 opens the air communicating valve 88 at a time t6 and then closes thecirculation valve 87 at a time t7.

Then, when the wiping operation has been started at a time t8, themaintenance controller 45 moves the four ink-jet heads 1 upward by amoving mechanism, not shown, and then moves the four wiper members 32 inthe main scanning direction along the ejection faces 2 a respectivelyfacing thereto while holding distal ends of the respective wiper members32 in contact with the respective ejection faces 2 a. This operationremoves the excessive ink adhering to the ejection faces 2 a by thepurging operation and recovers or arranges the state of the ink meniscusformed in the ejection openings 108. After the ejection faces 2 a havebeen wiped at a time t9, the maintenance controller 45 returns the fourwiper members 32 and the ink-jet heads 1 to their respective originalpositions, and the circulation-and-purging controller 44 opens thecirculation valve 87 at a time t10, and the wiping operation iscompleted.

As described above, according to the ink-jet printer 101 as the presentembodiment, the air bubbles, the foreign matters, and the like remainingin the ink inlet channel 72 can be discharged into the sub-tank 80 bythe ink circulation while preventing the ink from leaking from theejection openings 108. Further, the circulation valve 87 is closed inthis state to momentarily increase the pressure in the ink inlet channel72, whereby the ink in the ink inlet channel 72 flows into the inkoutlet channels 75 so as to be discharged from the ejection openings108. In this operation, a relatively high pressure is applied to all theejection openings 108 from the start of the purging operation todischarge the ink in the ejection openings 108. Accordingly, it ispossible to efficiently discharge the thickened ink in the ejectionopenings 108, the air bubbles, and the foreign matters, and it ispossible to prevent the ink from being discharged needlessly. Further,in the above-described embodiment, the unit-time supply amount isreduced during the purging period by stopping the driving of the purgingpump 86. Thus, the unit-time supply amount at the end of the purgingperiod is less than that during the ink circulation, whereby thepressure in the ink inlet channel 72 is lowered. Accordingly, even wherea meniscus withstanding pressure of the meniscus formed in the ejectionopenings 108 has been lowered because the ink discharged from theejection openings 108 in a previous purging operation has adhered todefining portions of the ejection openings 108, it is possible toprevent the ink from leaking from the ejection openings 108 after theend of the purging period.

Further, since the unit-time supply amount is reduced by stopping thedriving of the purging pump 86, the unit-time supply amount can beeasily reduced. Further, since the pressure in the ink inlet channel 72is lowered, the purging operation can be quickly completed.

Further, since the negative pressure is produced in the sub-tank 80 byclosing the air communicating valve 88 during the ink circulation tointerrupt the communication of the sub-tank 80 with the ambient air, theink of the ink inlet channel 72 is sucked into the sub-tank 80 via thedischarge channel 73 and the ink returning tube 83, making moredifficult for the ink in the ink inlet channel 72 to flow into the inkoutlet channels 75. As a result, the ink is less likely to leak from theejection openings 108.

Further, in the above-described embodiment, since the circulation valve87 is closed, and the air communicating valve 88 is opened at the sametime when the purging operation is started, the pressure of the insideof the sub-tank 80 forcibly becomes the atmospheric pressure, therebypreventing the pressure in the sub-tank 80 from lowering in accordancewith the discharging of the ink. Accordingly, since the ink in the inkinlet channel 72 is not sucked into the sub-tank 80 via the dischargechannel 73, the ink supply of the purging pump 86 to the ink outletchannels 75 is not hindered. As a result, it is possible to prevent theink discharging from the ejection openings 108 from being unstable orstopped.

Further, in the above-described embodiment, since the circulation valve87 is opened and the air communicating valve 88 is closed during thepurging period, the ink discharging from the ejection openings 108 isstopped, and the negative pressure is produced in the sub-tank 80.Accordingly, it is possible to quickly stop discharging the ink from theejection openings 108, and it is possible to prevent the ink fromleaking from the ejection openings 108 after the end of the purgingperiod.

Further, in the above-described embodiment, the circulation valve 87 iscompletely closed after the end of the purging operation. Accordingly,it is possible to prevent the ink having adhered to the ejection face 2a by the purging operation from being sucked into the ejection openings108 by, e.g., a water head difference between the ink-jet head 1 and thesub-tank 80.

Further, in the above-described embodiment, the wiping operation isperformed after the end of the purging operation. Accordingly, it ispossible to remove the ink and the foreign matters adhering to theejection faces 2 a and to recover or arrange the state of the inkmeniscus of the ejection openings 108.

Further, in the above-described embodiment, the resin film 76 partlyconstitutes the inner wall face of the ink inlet channel 72, and theresin film 78 partly constitutes the inner wall face of the dischargechannel 73. Thus, it is possible to efficiently restrain the changes ofthe ink pressures in the ink inlet channel 72 and the discharge channel73. Accordingly, the ink can be supplied to the individual ink channelsat a stabilized pressure. Further, when the resin films 76, 78 aredeformed in the ink circulation, a volume of the channel increases,lowering the pressure in the sub-tank 80. Accordingly, the ink is lesslikely to leak from the ejection openings 108.

<Modification>

There will be next explained a modification of the present embodiment.In the above-described embodiment, the driving of the purging pump 86 isstopped before the purging operation is stopped, but the presentinvention is not limited to this embodiment. For example, as shown inFIG. 12, the purging operation may be stopped by opening the circulationvalve 87, closing the air communicating valve 88, and stopping thedriving of the purging pump 86 at the same time at a time t5′. Where theprinter 101 is configured in this manner, it is easier to execute thecontrol for stopping the purging operation. Since there is a time delayuntil the purging operation is stopped after the circulation valve 87 isopened and the air communicating valve 88 is closed, the unit-timesupply amount is reduced in that period.

While the embodiment and the modification of the present invention havebeen described above, it is to be understood that the invention is notlimited to the details of the illustrated embodiment and modification,but may be embodied with various changes and modifications, which mayoccur to those skilled in the art, without departing from the spirit andscope of the invention. For example, in the above-described embodiment,the circulation valve 87 is selectively opened or closed, but a channelcontrolling valve capable of changing the channel resistance value atany value may be employed as the circulation valve 87. In this case, thechannel controlling valve may change the channel resistance value so asto change the channel resistance value stepwise or continuously.Further, the circulation valve 87 does not need to close the ink channelcompletely. Further, in the above-described embodiment, the channelresistance value of the ink returning tube 83 is adjusted by controllingthe circulation valve so as to reduce a cross-sectional area of the inkchannel of the ink returning tube 83, but, in order to adjust thechannel resistance value of the ink returning tube 83, an outercircumferential face of the ink returning tube 83 may be pinched by apinching member to deform the ink returning tube 83 so as to reduce thecross-sectional area of the ink channel of the ink returning tube 83.

Further, in the above-described embodiment, when the air communicatingvalve 88 is closed, the communication of the inside of the sub-tank 80with the ambient air is completely interrupted, but the inside of thesub-tank 80 and the ambient air may communicate with each other througha slight clearance in a state in which the air communicating valve 88 isclosed, as long as a negative pressure is produced in the sub-tank 80during the ink circulation.

Further, in the above-described embodiment, the air communicating valve88 is closed during the ink circulation and opened during the purgingperiod, but may be opened and closed at any timings. For example, theair communicating valve 88 may be closed during all the ink circulationperiod and the purging period and may be closed for at least a part ofthe ink circulation period and the purging period. It is noted that theair communicating valve 88 is preferably closed during a period forrestraining the ink from leaking from the ejection openings 108.Further, the ink supply unit 10 may not include the air communicatingvalve 88.

Further, in the above-described embodiment, the wiping operation isperformed in the maintenance operation, but the wiping operation may beomitted.

In addition, in the above-described embodiment, the resin film 76 partlyconstitutes the inner wall face of the ink inlet channel 72, and theresin film 78 partly constitutes the inner wall face of the dischargechannel 73, but the reservoir unit may not include at least one of theresin films 76, 78.

Further, in the above-described embodiment, the ink-flow amount from thepurging pump 86 per unit time during the ink circulation is smaller thanthe meniscus-break ink-leakage amount, but the ink-flow amount may beequal to or larger than the meniscus-break ink-leakage amount as long asan amount of the ink leaking from the ejection openings 108 during theink circulation is very small. For example, where the ink is leakingfrom only a small number of the ejection openings, the meniscus breakoccurs in the ejection openings, but an amount of the leaking ink is sosmall that effects for preventing the ink from being consumed needlesslycan be obtained as a whole.

Further, in the above-described embodiment, the purging pump 86 isprovided by the three-phase diaphragm pump as one of the volume pumps,but may be another volume pump such as a tube pump and may be a pumpother than the volume pump such as an impeller pump.

Further, in the above-described embodiment, each actuator unit 21 isprovided by the unimorph piezoelectric actuator, but the actuator unitmay be constituted by bimorph piezoelectric actuators. Further, thepresent invention may be applied to a thermal liquid ejection apparatusincluding heating elements.

Further, in the above-described embodiments, the circulation valve 87 isprovided on the ink returning tube 83, but as shown in FIG. 13, acirculation valve 187 may be provided on the discharge channel 73 at aposition in a predetermined area from the outlet opening 73 a to adjustthe channel resistance value of the discharge channel 73. Where theprinter is configured in this manner, the circulation valve 187 ispositioned near the ejection openings 108, making it possible to quicklystart discharging the ink from the ejection openings 108 in the purgingoperation. It is noted that the term “in the predetermined area from theoutlet opening 73 a” means an area from the outlet opening 73 a to aposition at which the discharge channel 73 is branched from the inkinlet channel 72 (i.e., in the discharge channel 73).

The present invention is applicable to a liquid ejection apparatusconfigured to eject liquid other than the ink. Further, the presentinvention is applicable to a facsimile machine, a copying machine, andthe like, in addition to the printer.

What is claimed is:
 1. A liquid ejection apparatus comprising: a liquidejection head including: an inlet opening into which liquid flows; anoutlet opening from which the liquid having flowed into the inletopening flows; an inside channel communicating the inlet opening and theoutlet opening with each other; and a plurality of ejection openingsthrough which is ejected the liquid having flowed through a plurality ofindividual channels that are branched from the inside channel; a tankstoring the liquid to be supplied to the liquid ejection head; a supplychannel communicating the tank and the inlet opening with each other; areturn channel communicating the tank and the outlet opening with eachother; a supply device configured to supply the liquid in the tank tothe inside channel via the supply channel; an adjusting deviceconfigured to adjust a channel resistance value of the return channelbetween a predetermined minimum value and a predetermined maximum value;and a controller configured to control the supply device and theadjusting device, wherein the controller is configured to start a liquidcirculation control for circulating the liquid through the supplychannel, the inside channel, and the return channel in order bycontrolling (i) the adjusting device such that the channel resistancevalue is less than the predetermined maximum value and (ii) the supplydevice to supply the liquid into the inside channel, wherein, when theliquid is circulated by the liquid circulation control, the controllerstarts a liquid discharge control for discharging the liquid from theplurality of the ejection openings by increasing the channel resistancevalue to a value larger than the channel resistance value in the liquidcirculation control, wherein, when the liquid is discharged by theliquid discharge control, the controller starts a liquid-dischargestopping control for stopping the discharge of the liquid from theplurality of the ejection openings, by decreasing the channel resistancevalue to a value less than the channel resistance value in the liquiddischarge control, wherein the controller is configured to control thesupply device such that a unit-time supply amount that is an amount ofthe liquid supplied to the inside channel per unit time at a time whenthe discharge of the liquid from the plurality of the ejection openingsis stopped by the liquid-discharge stopping control is less than aunit-time supply amount in the liquid circulation control, and whereinthe controller is configured to start to control the supply device todecrease the unit-time supply amount at the same time when thecontroller starts to control the adjusting device to decrease thechannel resistance value in the liquid-discharge stopping control. 2.The liquid ejection apparatus according to claim 1, wherein thecontroller is configured to control the supply device such that theunit-time supply amount in the liquid circulation control becomes apredetermined amount that does not cause the liquid to be dischargedfrom the plurality of the ejection openings.
 3. The liquid ejectionapparatus according to claim 1, wherein the controller is configured todecrease the unit-time supply amount by controlling the supply device tostop supplying the liquid.
 4. The liquid ejection apparatus according toclaim 1, further comprising an air communication device controlled bythe controller so as to communicate an inside of the tank with anambient air or interrupt the communication of the inside of the tankwith the ambient air, wherein the controller is configured to controlthe air communication device such that the communication of the insideof the tank with the ambient air is interrupted in at least a part of aperiod of the liquid circulation control.
 5. The liquid ejectionapparatus according to claim 4, wherein the controller is configured tocontrol the air communication device such that the inside of the tankcommunicates with the ambient air in at least a part of a period of theliquid discharge control.
 6. The liquid ejection apparatus according toclaim 5, wherein the controller is configured to control the adjustingdevice and supply device to perform the liquid-discharge stoppingcontrol such that the channel resistance value in the liquid-dischargestopping control is less than the channel resistance value in the liquiddischarge control and such that the inside of the tank is interruptedfrom the ambient air.
 7. The liquid ejection apparatus according toclaim 1, wherein the liquid ejection head has an ejection face havingthe plurality of the ejection openings formed therein, and wherein theliquid ejection apparatus further comprises a wiping device configuredto wipe the ejection face when the discharge of the liquid from theplurality of the ejection openings is stopped.
 8. The liquid ejectionapparatus according to claim 1, wherein at least a part of inner wallfaces of the inside channel and the supply channel is formed of aflexible material.